Ray Aldridge on sat 6 nov 99
At 04:55 PM 11/5/99 EST, you wrote:
>----------------------------Original message----------------------------
>The question is - how much of the Cadmium is perfectly encapsulated. There
>is no doubt in my mind that if all the Cadmium is encapsulated in a zircon
>crystal there will be no release. There is bound to be some Cadmium that is
>not perfectly encapsulated - how much and does it vary from batch to batch
>is our concern if those stains are to be used in glazes in contact with
>food.
>
Ron, evidently I was unclear in the way I stated my question. I'll try
again. If Hamer is correct and (as he implies) cadmium disappears from a
glaze that is not fired quickly and protected from oxidation, then perhaps
inperfectly encapsulated cadmium is no longer in the glaze and need not
concern us-- in much the same manner that the danger of lead leaching may
be discounted in a C10 reduction glaze. Or do you have information that
the cadmium which does not color a glaze remains in solution as some other
form of the metal?
It's good advice to have the glaze tested, though the pigment is so
expensive that I wouldn't want to use it for anything except accents. But
can anyone point me to a reference in which a glaze colored with
encapsulated cadmium actually released any significant amount of the metal?
I understand that just because we can't find such a report does not mean
that the colorant is safe, but I would think that the developers of these
colorants must have done some sort of testing before releasing them to the
market.
I suppose what I'm wondering about here is the assumption that because
cadmium-bearing china paints can release significant amounts of the metal,
then it follows logically that encapsulated cadmium has the same associated
hazards.
I understand the motivation for telling folks to play it safe, but in fact,
no one who has commented on this matter really has even the foggiest idea
whether these pigments are safe or dangerous, so far as I can tell. I
don't either, but if someone asked me, I'd tell them that cadmium is toxic,
that low-fire glazes containing cadmium have been shown to leach
significant levels of the metal, but that I had no idea whether or not this
was true of the encapsulated stains when used in a high temperature glaze.
The advice to have glazes made with these pigments tested is good for the
individual potter who has that specific glaze, but is really of little use
to the general discussion of whether or not these glazes *are,* *are not,*
or *might be* dangerous. Until, of course, someone has a hightemp glaze
bearing these stains analyzed and it's leaching cadmium. That would at
least settle the question of whether or not these pigments *might be*
dangerous, which is why I asked if anyone could cite a verifiable report of
such an outcome.
I guess I'd better do some research. Either way, best to know the truth.
Ray
Aldridge Porcelain and Stoneware
http://www.goodpots.com
Ray Aldridge on sat 6 nov 99
At 04:58 PM 11/5/99 EST, you wrote:
>----------------------------Original message----------------------------
>Ray Aldridge wrote:
>
>>This is something I've wondered about. Hamer calls these cadmium colors
>>"fugitive" and says that the red is a cadmium selenide-- that the selenium
>>volatizes rapidly and must be fired quickly and protected from oxidation or
>>it disappears from the glaze.
>>
>>So my question is this: how could these colors survive a high fire unless
>>the protective encapsulation retains its integrity? If they can retain
>>their integrity in the violently active medium of a molten glaze at high
>>temperature, how likely is it that a mild acid would breach this integrity?
>>
>>Finally, does anyone have any actual verifiable evidence that any glaze
>>made with these colors has actually leached cadmium?
>>
>>Ray
>>
> Ray, Hammer and Hamer are referring to plain old CdSe and CdS with their
>comments.
Exactly. I really was unclear, wasn't I? The point I was trying to make
is that if there is any danger of these pigments leaching, then almost
certainly it would be in the form Hamer is talking about, and not in the
encapsulated form, which must (it seems to me) retain its color because it
does *not* go into solution. This conjecture is supported by some
discussion in the archives on the difficulties of getting a transparent
color with these stains.
These inclusion stains are a horse of a different color. I
>don't know how they work--one of these days I'll see if I can find
>Cerdec's patent--but just the fact they are stable at high temperatures
>indicates they are doing something different to get their colors. I
>would guess they are microencapsulating in a very high melting frit while
>heavily reducing--say a frit that will take cone 20 or so. Whether that
>something different also makes them resistant to leaching is something I
>have no idea about. Who says the mechanism for retaining color at 1200 C
>and providing leach resistance to room temperature acids are the same?
I would think they would be very similar in this case, given the
terminology used-- "encapsulation."
I
>certainly wouldn't think they were. And I could certainly propose
>mechanisms by which they would leach out even though they retain their
>color stability at high temperature. There's not much point in that
>though; it would be pure speculation.
However, since I can't imagine a mechanism by which an object (a grain of
encapsulated cadmium, say) could resist solution in a glaze at 2300
degrees, but be readily dissolved by roomtemp acetic acid, I would be very
interested in such a speculation, if it were at all plausible.
>
>Nevertheless, since you are now putting cadmium into a glaze, U.S.
>federal regulations require you to test to be sure it doesn't leach out
>if you are putting it on a surface that could possibly be used for food.
>I'm sure the first person to run the required bank of tests on these
>stains will let the list know. That won't be me. I don't have any plans
>to use them.
Do you know of a net resource that contains this regulation? I'd like to
see the actual language.
I looked at the archives, and found a couple of interesting posts:
------------
"If these are cadmium &/or selenium pigments enclosed in zirconium
silicate crystals referred to as "inclusion pigments" dev. by
Degussa in Germany (?) & sold USA by Cerdec - if that's what you
are referring to, then yes I think they are quite safe all the
way around. I work w/ them & fire C/10 OX. I have had four
bases professionally tested and no cadmium release was detected.
Mfgr. literature describes these incl. pigmts as "thermally &
chemically" stable. NOTE: Do NOT ball mill these stains -
apparently this would damage the crystal structure &
release the stain. I know nothing about using them at lower
temps but see no reason why they would not also be safe.
Also they survive reduction firing just fine but w/ a
slight graying of the color.
If what I describe is NOT what you have encountered, then I
have no answer. I'd be interested to know. Karen Gringhuis"
----------------
and:
----------------
"A friend of mine , Gordon Ward, uses one of the commercial glazes which
has encapsulated cadmium as a colorant. He uses it as an overglaze
decoration.
He was also unsure as to wheter the cadmium would leach out of the fired
glaze.
He had it tested at a laboratory and they found no leaching. At least not
with
his base glaze.
Gordon fires at cone 10 in light reduction.
If your worried it would be best to have it tested for your specific
circumstances.
Hope this helps.
Michael Redwine"
-------------
I also saw a post in which Monona said she was trying to contact the folks
who sell the stain in the U.S., but I couldn't find out if she'd had any luck.
Ray
Aldridge Porcelain and Stoneware
http://www.goodpots.com
Michael Banks on sun 7 nov 99
Ray Aldridge wrote: (abridged)
> However, since I can't imagine a mechanism by which an object (a grain of
> encapsulated cadmium, say) could resist solution in a glaze at 2300
> degrees, but be readily dissolved by roomtemp acetic acid, I would be very
> interested in such a speculation, if it were at all plausible.
>
Your comment may be true Ray, but it may depend on the chemistry of the
glaze to what degree the zircon carrier resists solution. But first, for
those interested in the ins and outs of red, orange, pink and yellow cadmium
inclusion stains, I advise a visit to the Web Site:
http://www.cerdec.com/products/CadmiumInclusion.html This has
photomicrograph of the actual zircon carrier crystals with their Cd-Se-S
payload.
One of the manufacturer/distributors of these stains, Cerdec Corporation in
addition to warning that the stains should not be milled or ground (which
releases the cadmium sulpho selenide colour from encapsulation), recommends
in a data sheet in my possession that the stains are less suitable for
glazes rich in alkalis. This recommendation takes on some significance when
the solubility of zirconium in natural magmas is taken into account.
Zircon (ZrSiO4) is a very stable mineral, resistant to many forms of
chemical attack and with a melting point in excess of 2500 degrees C.
Zircon crystals are usually the first mineral to precipitate from molten
granite magma and survive high-grade metamorphism (where rocks are dragged
down to great depths and subjected to enormous pressure and high
temperatures). Individual zircon crystals are known to have been involved
in many cycles of granite melts, with periods of being liberated by erosion
and weathering in between, going from granite to sand, to sandstone, then
dragged down into the earth and its' matrix forming granite magma again.
Some zircons have been dated as being older than the oldest rocks known, the
granite and sandstone which once held them have long gone and they can be
pulled out of a granite rock 1000 times younger! Zircon is one tough
dude...
The problem that zircon has in stoneware glazes is that these are more
alkaline, more fluid and hotter than granite magma. One or two percent of
zircon opacifier added to a glaze dissolves in it. This is the reason that
you need to add at least 3% before any noticeable opacifying effect is
noted, more if the glaze is alkali rich. You have to exceed the particular
zirconium saturation point by adding more zircon. And in nature too, the
zirconium content of alkaline magmas is higher than regular granite
(reflecting solubility) and extremely alkaline rocks like nepheline syenites
are extremely high in Zr, reflecting the ability of these magmas to dissolve
large amounts of zircon from the source region.
So, what happens when you add Cd encapsulated inclusion stain to your glaze.
Well, some of it will dissolve, less if the glaze already is opacified with
some zircon (so the glaze is saturated in Zr). But more of the stain will
dissolve if the glaze is very alkaline, even to the point that the Cd colour
will fade or vanish. So this is the clue, if the stain fades, the zircon
carrier is dissolving and Cd may be accumulating in your flue. As for
leaching into food, the manufacturers claim very good safety. But I
wouldn't let the stain project above the gloss surface of foodware if I were
you.
A salutary tale here: I one mixed up some Cd encapsulated stain with alkali
frit, water and some clay in a jar. A couple of months later I opened the
jar and Whew!, got a putrid whiff of very nasty smelling gas which I would
bet money had a lot of sulphur, selenium and maybe even cadmium in it. This
I take to be evidence that even alkaline water at room temp can release the
Cd stain. So maybe here's a mechanism after all Ray.
Michael Banks,
Nelson,
New Zealand
Ron Roy on sun 7 nov 99
Hi Ray,
I think I answered most of your questions in my reply to Earl.
It may be so that the manufacture has tested for Cadmium release - In fact
I am sure of it. I am also sure that if there was no release we would know
that - I think there is some release - the question is how much and is it
the same each time?
RR
>>----------------------------Original message----------------------------
>Ron, evidently I was unclear in the way I stated my question. I'll try
>again. If Hamer is correct and (as he implies) cadmium disappears from a
>glaze that is not fired quickly and protected from oxidation, then perhaps
>inperfectly encapsulated cadmium is no longer in the glaze and need not
>concern us-- in much the same manner that the danger of lead leaching may
>be discounted in a C10 reduction glaze. Or do you have information that
>the cadmium which does not color a glaze remains in solution as some other
>form of the metal?
>
>It's good advice to have the glaze tested, though the pigment is so
>expensive that I wouldn't want to use it for anything except accents. But
>can anyone point me to a reference in which a glaze colored with
>encapsulated cadmium actually released any significant amount of the metal?
> I understand that just because we can't find such a report does not mean
>that the colorant is safe, but I would think that the developers of these
>colorants must have done some sort of testing before releasing them to the
>market.
>
>I suppose what I'm wondering about here is the assumption that because
>cadmium-bearing china paints can release significant amounts of the metal,
>then it follows logically that encapsulated cadmium has the same associated
>hazards.
>
>I understand the motivation for telling folks to play it safe, but in fact,
>no one who has commented on this matter really has even the foggiest idea
>whether these pigments are safe or dangerous, so far as I can tell. I
>don't either, but if someone asked me, I'd tell them that cadmium is toxic,
>that low-fire glazes containing cadmium have been shown to leach
>significant levels of the metal, but that I had no idea whether or not this
>was true of the encapsulated stains when used in a high temperature glaze.
>The advice to have glazes made with these pigments tested is good for the
>individual potter who has that specific glaze, but is really of little use
>to the general discussion of whether or not these glazes *are,* *are not,*
>or *might be* dangerous. Until, of course, someone has a hightemp glaze
>bearing these stains analyzed and it's leaching cadmium. That would at
>least settle the question of whether or not these pigments *might be*
>dangerous, which is why I asked if anyone could cite a verifiable report of
>such an outcome.
>
>I guess I'd better do some research. Either way, best to know the truth.
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
John Hesselberth on sun 7 nov 99
Ray Aldridge wrote:
>
>However, since I can't imagine a mechanism by which an object (a grain of
>encapsulated cadmium, say) could resist solution in a glaze at 2300
>degrees, but be readily dissolved by roomtemp acetic acid, I would be very
>interested in such a speculation, if it were at all plausible.
>
Well for one, the encapsulated particle could crack/craze during cooling,
due to different expansion coefficients between it and the glaze
surrounding it, thereby releasing the Cd for leaching.
>Do you know of a net resource that contains this regulation? I'd like to
>see the actual language.
Well I can give you an internet reference by which the FDA tests to
decide whether or not to impound or take legal action for lead. While I
haven't personally found an internet reference as to what is required of
manufacturers, I would think it would be smart to be assured that your
work passes the tests the FDA may use. It also goes into detail on
definitions of hollowware, flatware, cups, etc. and specifies how pots
must be labeled if it is unsuitable for food use.
Go to www.fda.gov and search for CPG 7117.07 The specific URL is about
2 lines long so I won't try to reproduce it here.
I haven't found a similar reference for cadmium.
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
"It is time for potters to claim their proper field. Pottery in its pure
form relies neither on sculptural additions nor on pictorial decorations.
but on the counterpoint of form, design, colour, texture and the quality
of the material, all directed to a function." Michael Cardew in "Pioneer
Pottery"
Ray Aldridge on mon 8 nov 99
At 05:25 PM 11/7/99 EST, you wrote:
>----------------------------Original message----------------------------
>Ray Aldridge wrote: (abridged)
>> However, since I can't imagine a mechanism by which an object (a grain of
>> encapsulated cadmium, say) could resist solution in a glaze at 2300
>> degrees, but be readily dissolved by roomtemp acetic acid, I would be very
>> interested in such a speculation, if it were at all plausible.
>>
>
>Your comment may be true Ray, but it may depend on the chemistry of the
>glaze to what degree the zircon carrier resists solution. But first, for
>those interested in the ins and outs of red, orange, pink and yellow cadmium
>inclusion stains, I advise a visit to the Web Site:
>http://www.cerdec.com/products/CadmiumInclusion.html This has
>photomicrograph of the actual zircon carrier crystals with their Cd-Se-S
>payload.
>
(snip)
Michael, excellent and informative post-- thanks. I have a couple of
clarifying questions.
>some zircon (so the glaze is saturated in Zr). But more of the stain will
>dissolve if the glaze is very alkaline, even to the point that the Cd colour
>will fade or vanish. So this is the clue, if the stain fades, the zircon
>carrier is dissolving and Cd may be accumulating in your flue.
Flue? Does this mean that unencapsulated cadmium vaporizes from a high-temp
glaze?
>
>A salutary tale here: I one mixed up some Cd encapsulated stain with alkali
>frit, water and some clay in a jar. A couple of months later I opened the
>jar and Whew!, got a putrid whiff of very nasty smelling gas which I would
>bet money had a lot of sulphur, selenium and maybe even cadmium in it. This
>I take to be evidence that even alkaline water at room temp can release the
>Cd stain. So maybe here's a mechanism after all Ray.
>
>
I wonder if this might be due to the thought Ron Roy posted, which is that
the stains might not be pure-- that some unencapsulated cadmium and
selenium might be found in the stain as it comes from the manufacturer. (I
noticed that on the manufacturers' site, they mentioned that a strong smell
might be detected the first time a container of pigment is opened.)
However, if this is true, does this contamination remain in the glaze at
high temps?
Ray
Aldridge Porcelain and Stoneware
http://www.goodpots.com
Ray Aldridge on mon 8 nov 99
At 05:34 PM 11/7/99 EST, you wrote:
>----------------------------Original message----------------------------
>Ray Aldridge wrote:
>
>>
>>However, since I can't imagine a mechanism by which an object (a grain of
>>encapsulated cadmium, say) could resist solution in a glaze at 2300
>>degrees, but be readily dissolved by roomtemp acetic acid, I would be very
>>interested in such a speculation, if it were at all plausible.
>>
>
>Well for one, the encapsulated particle could crack/craze during cooling,
>due to different expansion coefficients between it and the glaze
>surrounding it, thereby releasing the Cd for leaching.
Sounds plausible to me. Maybe Michael Banks will comment on this-- though
his post on the durability of zircon crystals might apply.
>
>
>>Do you know of a net resource that contains this regulation? I'd like to
>>see the actual language.
>
>Well I can give you an internet reference by which the FDA tests to
>decide whether or not to impound or take legal action for lead.
(snip)
>
>I haven't found a similar reference for cadmium.
>
The parallel reference can be found at the same site, as CPG 7117.06
However, this information does not pertain to any mandated testing program
for cadmium-bearing wares.
So far the only reference I've found leads me to believe that testing is
*not* mandatory:
http://www.fda.gov/opacom/morechoices/smallbusiness/blubook.htm#house.html
An excerpt:
"While food packaging materials are subject to regulation as "food
additives," FDA has generally not enforced the food additive
provisions on ordinary housewares. Such housewares include dishes,
flatware, beverage glasses, mugs, cooking utensils, cutlery, and
electrical appliances. This means that manufacturers have not been required
to submit data to the FDA showing that the materials used
are safe. They also are not required to pre-clear their housewares with
FDA. But housewares are not exempt from the general safety
provisions of the Federal Food, Drug, and Cosmetic Act. Regulatory actions
have been taken against cookware and ceramic dinnerware
containing leachable lead or cadmium."
The way this reads to me is that you would be held accountable for any
cadmium leaching in excess of the statutory allowance (which varies
according to the type of ware, see above guideline) but you would not be in
violation of any law if you do not test cadmium-bearing wares before
marketing them. The impression I've gotten from various Clayart posts is
that this testing is mandatory, and that failure to perform these tests
could lead to legal action, whether or not the ware was actually dangerous.
Of course, it might be stupid not to perform these tests, but so far I
haven't found any evidence that it's illegal.
Where did you originally hear about the regulations pertaining to cadmium
testing?
Ray
Aldridge Porcelain and Stoneware
http://www.goodpots.com
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